1. Field of the Invention
The present invention relates to an electric motor that has air purging function for preventing foreign substances from entering the inside of the electric motor.
2. Description of the Related Art
Electric motors are used, in some cases, in an environment in which foreign substances scatter. For example, a spindle head of a machine tool is disposed in a processing chamber for processing workpieces. The spindle head is used in an environment in which foreign substances such as chips occurring during cutting and cutting fluid scatter. The spindle head includes an electric motor for rotating a spindle. When foreign substances enter the inside of the electric motor, an insulation failure may occur in a coil, or a bearing function may be impaired. Thus, it is preferable that the electric motor has a mechanism for preventing foreign substances from entering the inside of the electric motor. An electric motor in which, for example, a sealing member is provided between a housing and a rotary shaft has been known. Further, an electric motor in which air is supplied between a housing and a rotary shaft has been known.
Japanese Unexamined Patent Publication No. 2007-105850 discloses an electric motor in which compressed air, which has been supplied to the inside of a housing, passes between a stator core and a rotor, and is supplied to a front housing. In this electric motor, the compressed air is injected toward the surface of a rotary shaft via an air exhaust passage that is formed so as to bypass a bearing.
Japanese Unexamined Patent Publication No. 2013-236473 discloses an electric motor that is provided with an air purging device attached to an end face of a housing, and discloses that this air purging device supplies air to a clearance between the inner peripheral surface of the air purging device and the outer peripheral surface of an output shaft.